1. Field:
This invention relates to communication systems, particularly telephone systems, and provides a random access, multiple station system in which AM transmitters and receivers are interconnected by conductors.
2. State of the Art:
Multiplexing techniques are well-known. Such techniques have been applied to various types of carrier transmission systems.
U.S. Pat. No. 3,573,379 discloses a communication system with both frequency and time division techniques. According to that patent, control information is carried in audio channels in the form of a time-divided binary pulse stream. When a call is made from one station to another, the receiving station is signalled that it is being called and on which channel. The transmitting frequency of the receiving station is selected after the call is received. U.S. Pat. No. 3,550,134 discloses a phase-locked loop, double carrier transmission system which includes a feedback loop from a voltage-controlled oscillator to a phase detector. U.S. Pat. No. 3,509,462 discloses a transceiver system in which the transmitter and receiver loops are independently phase-locked. U.S. Pat. No. 3,555,195 discloses a time multiplex system with phase-locked controls. U.S. Pat. No. 3,513,264 discloses a controlled, random access, communication system wherein access from one station to another is through a control center; each system has a transmitter and a receiver, each of which has a plurality of available channels. U.S. Pat. No. 3,519,747 teaches the use of tone codes with respect to time to control a communication system which includes conferencing capabilities.